Various methods for cleaning up sites contaminated with immiscible fluids, such as solvents, gasoline, diesel fuel and oils, include partial, in situ removal of the fluid from the soil subsurface. Current methods include boring a well into the subsurface and either recovering a fraction of the spilled fluid by skimming, or pumping groundwater out from below the spilled fluid to cause some portion of the fluid to collect in previously uncontaminated regions and then pumping the fluid out. In another method, the fluid is intercepted in a trench or drain constructed at a level below the spilled fluid.
These three methods are typically ineffective, cause further spread of the contaminants through the subsurface of the soil, and result in a large portion of the fluid remaining trapped in soil and groundwater. Further, such problems are compounded in the case of a spill of viscous oil. For example, the first method could lead to isolation of the fluid from the well, rendering the well useless for further recovery of fluid from a contaminated zone. The second method induces the flow of fluid into the zone previously occupied by groundwater. This spreads the spilled fluid downward and establishes new equilibrium conditions in the region While this permits some spilled fluid to be removed, additional removal requires the sequence be repeated so that the spilled fluid is driven to deeper and more extensive regions of the subsurface. A large volume of the spilled fluid will remain trapped as residual saturation in the new regions of contamination, significantly reducing the portion able to be recovered and requiring treatment of a large volume of contaminated water.
The art of producing petroleum product from a naturally occurring petroleum reservoir formation does not provide guidance for cleaning up a spill. Natural reservoirs are under pressure, relatively impermeable at their boundary, and typically contain dissolved gases, all of which tend to induce flow of petroleum product from the reservoir. In a fluid spill, there is no natural inducement or driving force causing flow of fluid from the subsurface. The driving forces which facilitate flow from a natural reservoir are simply not present to facilitate cleaning up a contaminated spill.
In cleaning up the spill, it is desirable to prevent further spread of the spill in the subsurface and into the groundwater zone. In contrast, natural reservoir formations have low permeability at the natural boundary which deters migration of the reservoir product. Some production techniques simply include separately removing water in a relatively uncontrolled manner primarily to prevent mixing of water into the oil product and not to prevent migration of either oil or water during production.
Therefore, what is needed is a method for the recovery of a spilled fluid which is capable of removing the spilled fluid from soil in situ, while at the same time preventing the spread of the spill.